There has heretofore been known a drive apparatus of a vehicle including a differential device through which an output of a drive power source, such as an engine or the like, is distributed to a first electric motor and an output member, and a second electric motor disposed between the output member and drive wheels. Such drive apparatus for a hybrid vehicle is disclosed for example in a Patent Documents 1, 3 and 5. It includes a differential mechanism being comprised of a planetary gear unit and performing a differential action for mechanically transmitting a major part of power outputted from the engine to drive wheels. A remaining part of power from the engine is electrically transmitted from the first electric motor to the second electric motor using an electrical path.
Thus, the drive apparatus operates a transmission of which shifting ratio is electrically changed, for example as an electrically controlled continuously variable automatic transmission. The drive apparatus is controlled by the control device so that the vehicle runs with the optimum operation state of the engine, thus improving fuel consumption, i.e., mileage.
Patent Document 1: JP 2003-127679A
Patent Document 2: JP 2001-339805A
Patent Document 3: JP 2003-301731A
Patent Document 4: JP 2002-89307A
Patent Document 5: JP 2004-270679A
In general, the continuously variable transmission has heretofore been known as a device for improving fuel consumption of a vehicle. A gear type power transmitting device such as a step variable automatic transmission has heretofore been known as a device having high transmitting efficiency. However, no power transmitting mechanism having such combined advantages has been put into practical use yet. For instance, the hybrid vehicle drive apparatus, disclosed in the above Patent Publication 1, includes the electrical path through which electric energy is transmitted from the first electric motor to the second electric motor, that is, a transmitting path through which a part of the vehicle drive force is transmitted in the form of electric energy. This inevitably causes the first electric motor to be made large-size with an increase in an output of the engine. Also, the second electric motor, driven with electric energy output from the first electric motor, is caused to increase in size. Thus, an issue arises with the occurrence of an increase in size of the drive apparatus.
Alternatively, since a part of the engine output is transmitted to the drive wheel after converted into electric energy once, the fuel consumption may be worsened depending on the running condition of the vehicle such as the high speed running. Similar problem occurs when the above power distributing device is used as the transmission of which shifting ratio is changed electrically, for example the electrically controlled CVT.
Meanwhile, with the drive apparatus for hybrid vehicle described above, there has heretofore been known a structure including a step-variable transmission disposed in a power transmitting path between an output member of a differential mechanism (electrically controlled continuously variable transmission) and drive wheels with a view to reducing a demanded capacity of the second electric motor when high drive torque is required to miniaturize the second electric motor. With such a vehicular drive apparatus, the output of the power drive force source is transferred through the two transmitting mechanisms such as the electrically controlled continuously variable transmission and the step-variable transmission, while establishing the total speed ratio of the drive apparatus based on the respective gear ratios of these transmitting mechanisms.
Further, in general, when a need arises for a vehicle drive force or engine brake greater than those required for the running of the vehicle on an even road, i.e., during the running of the vehicle on an ascending/descending road, a vehicular drive apparatus, having the step-variable transmission which is independently provided, operates so as to set a low vehicle speed side gear ratio (low gear) that is relatively larger in gear ratio than that set for the running of the vehicle on the even road or flat road. This allows the low gear to be maintained in phase up to a high vehicle speed in comparison to the gear position maintained for the vehicle running on the even road, thereby suppressing an upshift for thereby preventing a busy shift.
This similarly applies to a phase wherein the drive apparatus establishes the total speed ratio based on the respective gear ratios of the electrically controlled continuously variable transmission and the step-variable transmission. During the running of the vehicle on the ascending/descending road, for instance, the total speed ratio is set to the lower vehicle speed side gear ratio than that set for the running of the vehicle on the even road, suppressing the upshift for thereby preventing the busy shift.
However, with the electrically controlled continuously variable transmission functioning as the electrically controlled CVT, the first electric motor has a need to bear reaction torque depending on engine torque. Therefore, under a situation where the vehicle runs under high load of the engine like when the vehicle runs on the ascending road, reaction torque (load torque) born with the first electric motor increases, resulting in likelihood of a shortage occurring in the drive force depending on the performance of the first electric motor. From another point of view, in order to preclude the shortage in drive force during the running of the vehicle on the ascending road, the first electric motor needs to be increased in size.
Further, during the running of the vehicle on the descending road, the second electric motor is rendered operative as an electric power generator to convert kinetic energy to electric energy that is collected in a battery while achieving a regenerative brake due to power-generating resistance of the second electric motor for thereby obtaining a requisite drive force source brake. However, suppressing the upshift has resulted in likelihood of an increase in load torque of the second electric motor. Further, under a situation where the regeneration amount is unavailable to increase due to a full charge or the like of the battery, there has been a probability with a difficulty of obtaining the required drive force source brake.
Given this situation, with the vehicular drive apparatus in which the drive apparatus, enabled to address the issue of the drive apparatus for hybrid vehicle disclosed in Patent Publication 1, further includes an automatic transmission, it has been required to have a requisite drive force and drive force source brake while preventing the busy shift.
Further, with the hybrid vehicle disclosed in Patent Publication 3, the second electric motor is rendered operative as the electric power generator during the speed reduction running. This causes kinetic energy of the vehicle to be converted to electric energy for recovery to the battery, while causing power-generating resistance of the second electric motor to achieve the regeneration brake. When this takes place, a fuel supply to the engine is shut off causing the engine rotation speed to be zeroed or nearly zeroed for a reduction in engine drag for thereby increasing the regeneration amount. However, if the regeneration amount is unavailable to increase due to the full charge of the battery, there has been a probability with a difficulty occurring in obtaining a given drive condition and a target speed reduction magnitude set by a driver.
With the technology disclosed in Patent Publication 4, during the speed reduction running i.e., on-speed reduction running of the vehicle having an in-cylinder pressure variation suppression-based cylinder number variable engine, all the cylinders of the engine are brought into compression states when no regeneration brake is applied, thereby obtaining an engine brake effect. Meanwhile, when the regeneration brake is initiated, a part of the engine cylinders remaining inoperative are brought into in-cylinder pressure variation suppression states, i.e., decompression states. This causes a reduction in the engine braking effect to obtain a similar braking effect regardless of the existence or non-existence of the regeneration. However, changing the cylinder number of the engine and the regeneration amount allows the speed reduction magnitude to be controlled, resulting in likelihood of a difficulty arising in obtaining the given drive condition and the target speed reduction magnitude set by the driver.
Further, even with the vehicular drive apparatus, disclosed in Patent Publication 3, which is structured to address the issue of the drive apparatus for hybrid vehicle, likewise, there has been likelihood of a difficulty arising in obtaining the given drive condition and the target speed reduction magnitude set by the driver during the speed reduction running.
Patent Publication 5 discloses a technology of changing a cubic capacity of a combustion chamber to decrease a compression ratio of the engine during a regeneration for decreasing friction (drag) torque of the engine to improve a regeneration efficiency of an electric motor. Drag torque of the engine also varies depending on the engine rotation speed and it is likely that the lower the engine rotation speed, the less will be drag torque of the engine. So, if a uniform regeneration amount is set for the speed reduction running to allow the electric motor to perform the regeneration in accord with an engine state in increased engine drag torque, that is, in other words, a lessened level of the regeneration amount achieved by the electric motor, there has been likelihood of the occurrence of a deterioration in fuel consumption. This is because the regeneration amount is unavailable to increase even under the engine state available to obtain the increased regeneration amount.
Even with the vehicular drive apparatus structured to address the issue of the drive apparatus for hybrid vehicle disclosed in Patent Publication 3, there has been likelihood that if the electric motor uniformly performs the regeneration during the speed reduction running, the regeneration amount is unavailable to increase with a resultant deterioration in fuel consumption.
The present invention has been completed on the ground of the circumstances, described above, and has a first object to provide a control device for a vehicular drive apparatus, including an electrically controlled continuously variable shifting portion, composed of a differential mechanism operative to distribute an output of an engine to a first electric motor and a transmitting member and a second electric motor disposed in a power transmitting path between the transmitting member and drive wheels, and a transmission forming a part of the power transmitting path, which can be miniaturized in structure and/or have improved fuel consumption while preventing a busy shift.
It is a second object of the present invention to provide a control device for a vehicular drive apparatus, including a differential mechanism, operative to perform a differential action to distribute an output of an engine to a first electric motor and an output shaft, and a second electric motor disposed in a power transmitting path between the differential mechanism and drive wheels, which can be miniaturized in structure and/or have improved fuel consumption while improving a control performance on a speed reduction magnitude during the speed reduction running i.e., slow down running or deceleration running.
It is a third object of the present invention to provide a control device for a vehicular drive apparatus, including a differential mechanism, operative to perform a differential action to distribute an output of an engine to a first electric motor and an output shaft, and a second electric motor disposed in a power transmitting path between the differential mechanism and drive wheels, which can be miniaturized in structure and/or have improved fuel consumption while improving a fuel consumption during the speed reduction running.